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Math Help - Proof a of theorem

  1. #1
    Junior Member
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    Proof a of theorem

    Is this the correct way to prove (-a)b=-ab?

    Pf:
    Since -a+a=0, then (-a)b+ab=0b, so (-a)b+ab=0. Then (-a)b=-ab.


    I was wondering because the book I have uses the fact that -ab+ab=0 to create (-a)b+ab=-ab+ab and uses a theorem, a+c=b+c then a=b, to show (-a)b=-ab.
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  2. #2
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    Re: Proof a of theorem

    Your proof and the proof from the book are equally correct. I like your proof because it doesn't rely on that theorem.
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